'use strict'

let watermark = {}

let setWatermark = (str) => {
let id = 'watermark'

if (document.getElementById(id) !== null) {
	document.body.removeChild(document.getElementById(id))
}

let can = document.createElement('canvas')
can.width = 190
can.height = 150

let cans = can.getContext('2d');
cans.rotate(-20 * Math.PI / 180)
cans.font = '16px Vedana'
cans.fillStyle = 'rgba(200, 200, 200, 0.2)'
cans.textAlign = 'left'
cans.textBaseline = 'Middle'
cans.fillText(str, can.width / 16, can.height / 2)

let div = document.createElement('div');
div.id = id
div.style.pointerEvents = 'none'
div.style.top = '0'
div.style.left = '0'
div.style.position = 'fixed'
div.style.zIndex = '100'
div.style.width = document.documentElement.clientWidth + 'px'
div.style.height = document.documentElement.clientHeight + 'px'
div.style.background = 'url(' + can.toDataURL('image/png') + ') left top repeat'
document.body.appendChild(div);
	return id
}

// 该方法只允许调用一次
watermark.set = (str) => {
	let id = setWatermark(str)
	setInterval(() => {
		if (document.getElementById(id) === null) {
			id = setWatermark(str)
		}
	}, 500)
	window.onresize = () => {
		setWatermark(str)
	}
}

export default watermark